1. Field of the Invention
The present invention is related to an electronic circuit, and more particularly, to a signal generating apparatus.
2. Description of the Prior Art
A signal generator is capable of performing many functions. For example, the signal generator can perform a data/clock recovering process, modulating and demodulating frequency and phase, and generating a stable clock that can be synthesized into another frequency.
There are some tradeoffs that should be considered when designing a low jitter fast phase locking synthesizer. Specifically, when lowering the jitter and when increasing the tracking and locking of the phase it is well known that these two aspects of the signal generator are intrinsically in contradiction with each other. Furthermore, holding the operating duty-cycle of the clock signal at 50% is another critical issue in designing the synthesizer. In the prior art, a voltage controlled oscillator (VCO) is operated at doubled oscillating frequency (i.e., double the required frequency of the system), and then the oscillating frequency is divided in half in order to obtain the required oscillating frequency and the required 50% operating duty-cycle. However, when the requirement of oscillating frequency of the system clock is getting higher, the VCO is hard to oscillate at the doubled oscillating frequency.